1. Field of the Invention
This invention relates to a cassette for housing a radiation image storage panel therein. This invention particularly relates to a cassette provided with a small window, which is closed by a plate-like member containing lead and through which an identification mark put on the radiation image storage panel housed in the cassette is read.
2. Description of the Prior Art
X-ray photographic film has heretofore been known as a recording medium, on which a radiation image of an object, such as a human body, is recorded. Also, as a recording medium used for the same purposes, a sheet provided with a layer of a stimulable phosphor (hereinafter referred to as a radiation image storage panel or a stimulable phosphor sheet) has heretofore been known. Such radiation image storage panels are disclosed in, for example, U.S. Pat. Nos. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395. When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays, such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
A radiation image of an object is recorded on a radiation image storage panel by, for example, exposing the radiation image storage panel to radiation, which has passed through the object. The radiation image storage panel, on which the radiation image has been stored, is then scanned two-dimensionally with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored during exposure to the radiation. The light emitted by the radiation image storage panel, upon stimulation thereof, is photoelectrically detected. In this manner, an electric image signal representing the radiation image can be obtained.
By way of example, the radiation image storage panel or the X-ray photographic film described above is housed in a light-tight cassette, or a plurality of radiation image storage panels or plurality of sheets of X-ray photographic film are housed in a light-tight magazine. Each cassette serves to house a single panel-or sheet-shaped image recording medium, such as a radiation image storage panel, therein. In general, the cassette is constituted of a box member provided with an opening, through which a recording medium is to be fed into and out of the box member, at least at a portion, and a cover member, which opens and closes the opening. Also, a lead sheet for preventing back scattering of the radiation is secured to the entire area of the internal surface of the box member, which stands facing the back surface of the image recording medium.
In general, in cases where the cassette is used during a radiation image recording operation, the radiation image storage panel, or the like, on which a radiation image has been stored, is kept in the cassette, thereby prevented from being exposed to external light, and conveyed in this state into a darkroom.
In cases where radiation images of objects are recorded on radiation image storage panels, it is actually very important to control the radiation image storage panels, on which the radiation images of the objects have been recorded, in association with information giving specifics about the objects (e.g., in cases where the objects are patients, the name of each patient, the date of birth of each patient, and the like). However, for example, in cases where the radiation image recording operations are carried out for a large number of objects as in mass medical examinations, or the like, considerable time and labor are required to control the radiation image storage panels, on which the radiation images of the objects have been recorded, in association with the information giving specifics about the objects. Therefore, as disclosed in, for example, U.S. Pat. No. 4,498,005, a technique has been proposed wherein an identification mark is put on a radiation image storage panel and is detected with an optical means, a magnetic means, or the like, from the exterior of the cassette which houses the radiation image storage panel, the control of the radiation image storage panel being thereby facilitated.
Specifically, a label, or the like, having an identification mark, such as a bar code, is secured to the back surface of the radiation image storage panel (i.e. the surface opposite to the surface provided with a stimulable phosphor layer). Alternatively, an identification mark is directly put on the back surface of the radiation image storage panel. The radiation image storage panel is then housed in a cassette. A small window, through which the identification mark is to be read from the exterior of the cassette, is formed in the surface of the cassette, which surface stands facing the identification mark put on the radiation image storage panel. It is made clear which identification mark corresponds to which information giving specifics about the object. In this manner, the radiation image storage panel is easily controlled in association with the information giving specifics about the object. Also, by detecting the identification mark through the small window, it is possible to confirm that the radiation image storage panel has been housed in the cassette.
However, if the small window is merely formed in the back surface of the cassette in the manner described above, a lead sheet for preventing back scattering of radiation cannot be secured to the small window. Therefore, back scattering of the radiation occurs, and the image quality of the radiation image recorded on the radiation image storage panel cannot be kept high.
Accordingly, in cases where a cassette is provided with a small opening in the manner described above, the small opening is ordinarily closed by a plate-like member, such as a glass plate or a resin plate, which is substantially transparent and contains lead for preventing back scattering of the radiation.
The plate-like member, which is constituted of glass or a resin containing lead and secured to the cassette for the radiation image storage panel, is markedly weaker than glass and resins which are used for ordinary viewing windows. Therefore, the plate-like member is easily broken by small impact force. In order to prevent the plate-like member from breaking, close attention must heretofore be paid to the processing of the cassette.
Also, ordinarily, the plate-like member is secured by an adhesive to the cassette. Therefore, when the plate-like member breaks, fragments of the plate-like member and the adhesive remaining in the cassette must be removed completely, and thereafter a new plate-like member must be secured to the cassette. Considerable time and labor have heretofore been required to exchange the plate-like member with a new one.